MELs are a group of naturally occurring glycolipids that contain mannose and erythritol as the hydrophilic end, and fatty acids with different carbon chain lengths and degrees of unsaturation in their lipophilic end. They are classified under four groups as MEL-A, MEL-B, MEL-C and MEL-D depending on the acetylation of their hydroxyl groups. The properties of MELs are derived from their amphiphilic character, having potential use as biosurfactants, antimicrobial agents or vehicles for gene and drug delivery.
MELs can be produced by fermentation of a suitable microorganism, for example, Pseudozyma sp. produces MELs as a major component, whilst Ustilago sp. produces them as a minor component. Although MELs have been known for many years, they have only recently regained attention, particularly as biosurfactants, due to their environmental compatibility, mild production conditions, and structural diversity.
At present no suitable commercially viable method exists for either the isolation or purification of MELs from a crude fermentation medium, or the concentration or separation thereof into their individual groups (A, B, C and/or D) according to the degree of acetylation. In particular, there is a need for such a method which employs only renewable or “green” solvents and does not use potentially flammable or harmful organic solvents such as heptane or hexane.